15. A Poor Soul
This section of collapsed hallway is host to a symbiotic flora that requires a living host in order to procreate.

About thirty feet down the hall to your right is a goblin corpse in the fetal position next to the dead end of rubble. Its skin appears to be fuzzy and green, but as you get closer, you begin to realize that some kind of mold is growing on its rotting flesh.

Green Mold. If the corpse is disturbed or a creature comes within 5 feet of it, the green mold releases a 10 foot radius cloud of deadly spores. Creatures in the area of effect must make a DC 15 Constitution saving throw, or take 3d6 poison damage. The creature takes half damage on a successful saved.

Green Mold Disease. If a creature fails the Green Mold Constitution saving throw, roll a d20. On a roll of 16-20, the creature becomes infected. If infected, the creature’s Constitution score drops by 1 point after each long rest. They begin to grow green splotches on their skin, and die once they reach a Constitution score of 0. It counts as a disease in relation to removing it. Alternatively, suffering 20 hit points worth of fire damage in one round would also remove the condition.

Custom Alternatives. I essentially borrowed heavily from the Yellow Mold encounter in the Mines of Madness 5e playtest adventure. I just changed the name and added the disease to create the possibility of an ongoing issue for the player’s to encounter. Feel free to replace it with the Yellow Mold in the DMG, or any other form of natural surprise such as “the goblin’s a zombie!” or “the corpse explodes into several swarms of roaches!”.

16. The Rift
As the PCs approach the edge of the hall, read:

The hall ends in darkness ahead. The sound of rushing winds echo across the marble walls. As you approach, you see that the hall has opened to a gargantuan, underground rift so wide that the opposite end eludes your sight. Directly below you are several, small, stair stepped cliffs leading to another exposed marble hallway that hangs above the bottomless void.

Cliffs. Each cliff is only 5 feet high, meaning that outside of combat, the cliffs don’t require a check. In the midst of combat, the cliffs are a DC 5 Strength (Athletics) to climb.

As half the PCs have reached the second ledge, read:

The air around you seems to start humming, but you are quick to realize that the humming is actually a buzzing as a swarm of red, cat-sized insects fly in from the Rift.

Eight stirges swarm the PCs and attempt to drain them. If half the swarm is defeated, the rest retreat to the safety of the rift.

The Lower Hall. The hall below the cliffs is the primary entry point for the “Ancient Complex”. It is 15 feet away and 15 feet down from the ledge above. A character can make a DC 10 Strength (Athletics) check to climb to the Hall, or a DC 10 Strength (Athletics) check to jump to the hall followed by a DC 15 Dexterity saving throw to not roll off into the void below. They will take 2d6 falling damage from the jump, unless the character rolled a natural 20 on the Dexterity saving throw, which reduces the damage to 1d6 falling damage.